GO3
SZIL.IRD- CHALMERS REACTIOK
to be found n-ith the @-particle. If the readjustment, occurs independently of the nudear process, n-ill the energy be dissipated as very soft x-radiation or by ionization? We have not’ yet, received harmonious opinions on these points from colleagues more practiced in such considerations and prefer to delay discussion until more data on the chemical effects accumulate. REFERESCES (1) (2) (3) (4) (5) (6)
FEISRERG. E . L . : ,J. I’hys. (L-.S.S.R.) 4 , 423 ( 1 0 4 1 ~ . J. C.: Phys. Rev. 70, iS9 (19461. LIBBY,W ,F . : J. Ani. Chem. Soc. 62, 1030 (1940). SOX-EY, T. B . : J. - h i .Chem. Soc. 68, 2-111. reference ( S l l 5 1 , (1946). SUESS,F.: %. physik. Chem. B46, 312 (1939). WILLARD,J . E . : J. Phys. Colloid Chem. 52, 585 (1948). JACOBSEK,
T H E SZILARD-CHALAIERS REACTIOS I S THE CHAIITREACTISG PILE’ R . R . WILLI.\?rIS l l e p n i l m e n z of Chetiiistr u , T-nicerszty o,f .\-otre Dunre, AYotreDcrnie. Indiana lieceweti Octcibei 23, 1947 I. INTRODUCTIOX
The radiative capture of a neutron by a stable nucleus is an important nuclear reaction, which frequently gives rise t o a useful radioisotope. The chemical identity of t’he active isotope with the unchanged t’arget element frequently places serious limitations on the specific activities obtained by t’his reaction. The Szilard-Chalmers reaction, n-hich effects separation of the activated atoms from the target material by virtue of the gamma-ray recoil, can be used t’o enhance the specific activity of t’heactive material under favorable circumstances. This paper viill discuss certain factors which govern the usefulness of this cnrichment method, and in particular the effects of the intense radiation field of t,he chain-reacting pile. 11. SECESS.kRY COSDITIOSS FOR SZIL1RD-CHALJIERS
ESRICHMEKT
Keutron capture by a nucleus is accompanied b y the release of 8 or 9 m.e.v. of energy in the form of several energetic gamma quanta. The recoil energy I’rcsented at t h c Symposium o n Radiation (‘hemist1 tnd Phot ochcmistry if-hich \\-as held at the University of S o t r e Dame. S o t r e Danie. 1ndi:ni:i. .Tunc 24-2i, 1047. This document is based 011 ~ o r k perforiiied bj- .4. JV. =\tlsnison. Ci. E . 13oyt1, \\-. 1;. Colin, (;. .Jcnks, Q . I-.I,ai.son. 1V. 13. Leslie, J . IT-. R i c h t e r . 1:. 11. Tonipkins. ant1 R . It. WiI1i:ims. under Contract S o . Wi401-eng-37 for thc Atomic Energy I’i~ojcct, and t h r information covered therein m-ill appear in Division I\?, I-olume IS-B of t h e Sational iVuclear E n e r g y S e r i e s (Manhattan Project Technical Section) as part of thc contribution of t h e Argonne Sational Laboratory.
thus imparted to the capturing atom may be as much its one hundred times as great as the eiiergieq of the chemical bonds in which it participates, and Tre may expect the ioimation of an ionized, high--peed fi ngnient. Such fragments can be physically separated fiom the bombarded m a l erial, h i we shall be concerned only T\ ith chemical separations, for n liich the folloving conditions must hold: ( I ) The element must be c,ipnl)le of caistence in LLt lea-t t\vo mutually 5td)le and separable foims. ( 2 ) lcast tn-o of these formi must s h w lack of rapid iyotopic eschange. The ieactioiiq ~ v l i i ( Llltc “hot” htoni 01 fr,ignien~11 ill uiideigo depend t u soine extent on the nature of it. environment, and se\.eral v-orker, are engaged in a study of thebe pioresaea. For tlie present, hon-e\ er, the mole fruitful approach aftei cshoicc of ciic.iim iiicc- n hich fulfill condition. 1 and 2 :dm e , ib the trial and error method. Stany Seilard-Chalmer.; leactions arc kiiox\ 11, bevernl of u-hich n-ill be descrihed belov . -Ittempt. to enrich activitic. produced in the high Huh of iiie cl~~m-ieacting pile have l~roughtt o light third con4deration governing t h c effect 1renes5 of the proposed Szilai d--Chnlmer- enrichment. The high radiation field,- (principally y and neution) cdiiae marked cheniicd change5 in the bonib:mled compound. aside froni the effect. accompanying :tctiuation. That -wit I e:ic.tions may yield products -1niilaI t o those obtained in nctivation rwction- 1- t o be expected, since both type. air eisentially a decoinpozition by w(*it:t1ion The radiation decomposition can yield microscopic amounts of the chemical ioi in in v-hich tlie activity i i found, thu. diliitiiig the active isotope 11 1- a l w pohaible that tlie radiation field TI ill cause fin ther chemical re:ictions of tlie wp:+iable active i.otope nhich may change it t o a form n-hicll is no longei iep:irahle. although this effect is probably confined t o rather limited circumytance.. Establiqhment of a sucre-qfiil Szilard C‘halmei s enrichment reaction in eaperiinelits oi lon. flux or qhoi ;,ombardment thercfoie doe-: not en.ure It< success Trhen longei or more intenbe bombnrtlment- :ire employed. R d a t i o n decomposition may pi oduce prohibitive nniouiitq of inactive carriel a n d the fraction of activity scpai able may decrease. ‘I’he next section of this papei will preqent a seniiqunntitnt ire di-ciission of thebe two effect
